1. Field of the Invention
The present invention relates to an image display method and an image display apparatus using the method and, more particularly, to an image display method and an image display apparatus using the method, which are suitably used for displaying a two-dimensional partial image (non-stereoscopic image) and a three-dimensional partial image together (mixed display) or selectively displaying a two-dimensional image and a three-dimensional image using a parallax barrier method.
2. Related Background Art
As a conventional stereoscopic image display method, a stereoscopic image display method using a parallax barrier system (to be referred to as a parallax barrier method hereinafter) or the like is widely known.
The parallax barrier method is disclosed in S. H. Kaplan, "Theory of Parallax Barriers", J. SMPTE, Vol. 59, No. 7, pp. 11-21 (1952). With this method, a stripe image formed by at least alternately arranging right and left image portions obtained from a plurality of parallax images picked up at a plurality of view points is observed via a slit (called a parallax barrier) having predetermined aperture portions as parallax images corresponding to the two eyes of an observer, thus attaining stereoscopic viewing.
Furthermore, Japanese Laid-Open Patent Application Nos. 3-119889 and 5-122733 disclose a stereoscopic image display apparatus which electronically generates a parallax barrier using, e.g., a transmission type liquid crystal element and electronically controls to vary the shape and position of the parallax barrier so as to improve compatibility with a two-dimensional image (1-view point image) display apparatus.
FIG. 14 is a diagram showing the basic arrangement of a stereoscopic image display apparatus disclosed in Japanese Laid-Open Patent Application No. 3-119889. In this apparatus, an electronic parallax barrier 103 is arranged on a transmission type liquid crystal display element 101 for displaying an image via a spacer (transparent glass) 102 having a thickness d. On the transmission type liquid crystal display element 101, parallax images picked up from two or more directions are displayed as a vertical stripe image. On the electronic parallax barrier 103, a parallax barrier is formed at an arbitrary position on the barrier surface by designating X and Y addresses using a control means such as a microcomputer 104, thus allowing stereoscopic viewing according to the principle of the parallax barrier method.
FIG. 15 shows the arrangement of a display portion of a stereoscopic image display apparatus, which is disclosed in Japanese Laid-Open Patent Application No. 3-119889 and is constituted by a liquid crystal panel display and an electronic parallax barrier. The display portion comprises a glass (spacer) portion 102, polarizing plates 111, 118, 121, and 128, upper glass substrates 112 and 122, lower glass substrates 117 and 227, liquid crystal layers (TN) 115 and 125, common electrodes 113 and 123, pixel electrodes 116 and 126, and spacers 114 and 124, which constitute an electronic parallax barrier 103 and a liquid crystal panel display 110. That is, the two liquid crystal layers 115 and 125 are respectively sandwiched between the two polarizing plates 111 and 118 and the two polarizing plates 121 and 128. When a two-dimensional image is to be displayed by this apparatus, the display operation of the parallax barrier on the electronic parallax barrier 103 is stopped, so that the entire image display area is set in the transparent state, thereby realizing compatibility with a two-dimensional image display apparatus unlike in a conventional stereoscopic image display apparatus using the parallax barrier method.
FIGS. 16A, 16B, and 16C respectively show different parallax barrier patterns to be formed on the electronic parallax barrier in correspondence with different numbers of view points. As shown in FIGS. 16A to 16C, upon observation of a stripe image constituted by parallax images obtained from two view points, the width, A, of each light-shielding portion can be set to be equal to the width, B, of each light-transmitting portion. However, as the number of view points increases, the width of each light-transmitting portion decreases with respect to that of each light-shielding portion. That is, as the number of view points increases, the aperture ratio of the electronic parallax barrier decreases.
On the other hand, Japanese Laid-Open Patent Application No. 5-122733 discloses an arrangement which can display a parallax barrier pattern on only a partial area of an electronic parallax barrier 103 comprising a transmission type liquid crystal display element, and can display a three-dimensional image and a two-dimensional image together on a single screen, as shown in FIGS. 17A and 17B.
However, as disclosed in Haruo Isono, Minoru Yasuda, and Hideaki Sasazawa, "Liquid Crystal Parallax Barrier Type Three-dimensional Image Display", Journal of The Institute of Electronics, Information and Communication Engineers, C-II, Vol. J76-C-II, No. 1, pp. 24-30 (1993), in a three-dimensional image display apparatus using the parallax barrier method, the luminance of the screen lowers as the number of view points increases. FIG. 18 is a graph showing the relationship between the number of view points and the luminance/resolution in the stereoscopic image display apparatus using the parallax barrier method. Taking the luminance in the case of one view point, i.e., upon displaying a two-dimensional image as "1", the screen luminance upon displaying a three-dimensional image lowers as the number of view points increases, as shown in FIG. 18. More specifically, when the three-dimensional image is a stripe image obtained by synthesizing parallax images obtained from two view points, the screen luminance becomes 0.6; when the three-dimensional image is a stripe image obtained by synthesizing parallax images obtained from three view points, the screen luminance becomes as dark as about 0.4.
Therefore, in the three-dimensional image display apparatus disclosed in Japanese Laid-Open Patent Application No. 3-119889, the screen luminance drastically changes upon switching between three- and two-dimensional images.
Similarly, in the mixed display method of three- and two-dimensional partial images disclosed in Japanese Laid-Open Patent Application No. 5-122733, three- and two-dimensional image display areas have different image brightness levels, and images displayed on these areas are not easy to see.